Current Electricity Lecture Flashcards

Vocabulary flashcards covering the fundamental concepts of current electricity, including Ohm's law, resistivity, electronics drift, Kirchhoff's rules, and cells.

Electric Current

The net amount of charge flowing across a section of a conductor per unit time; for steady current, it is given by $I = q/t$, and more generally as $I = \frac{dQ}{dt}$.

Ampere

The SI unit of current, typically representing the order of magnitude of currents in domestic appliances.

Conductors

Materials, such as metals, where some electrons are practically free to move within the bulk material and develop electric currents when an electric field is applied.

Ohm’s Law

A basic law discovered by G.S. Ohm in 1828, stating that the potential difference $V$ across a conductor is proportional to the current $I$ flowing through it, expressed as $V = RI$.

Resistance ($R$)

The constant of proportionality for a conductor that depends on its material and dimensions; it is measured in ohms ($\Omega$).

Resistivity ($\rho$)

A constant of proportionality depending on the material of the conductor but not its dimensions, defined by the relation $R = \rho \frac{l}{A}$.

Current Density ($j$)

The current flowing per unit area normal to the direction of flow ($I/A$), with SI units of $\text{A/m}^2$.

Conductivity ($\sigma$)

The reciprocal of resistivity ($1/\rho$), which relates the current density to the electric field in the vector form \text{j} = \text{\sigma} \text{E}.

Drift Velocity ($v_d$)

The average velocity attained by electrons in a conductor due to an electric field, given by $v_d = \frac{e E \tau}{m}$.

Relaxation Time ($\tau$)

The average time interval between successive collisions of an electron with the fixed ions in a conductor.

Mobility ($\mu$)

The magnitude of the drift velocity per unit electric field ($\mu = \frac{|v_d|}{E}$), having SI units of $\text{m}^2/\text{Vs}$.

Temperature Co-efficient of Resistivity ($\alpha$)

The fractional increase in resistivity per unit increase in temperature, resulting in the relation \rho_T = \rho_0 [1 + \text{\alpha} (T-T_0)] for metals.

Electromotive Force (emf, $\varepsilon$)

The potential difference between the positive and negative electrodes of a cell in an open circuit (when no current is flowing through the cell).

Internal Resistance ($r$)

The finite resistance offered by the electrolytic solution inside a cell to the flow of current between its electrodes.

Kirchhoff’s Junction Rule

Based on the conservation of charge, it states that at any junction, the sum of the currents entering the junction equals the sum of the currents leaving it.

Kirchhoff’s Loop Rule

States that the algebraic sum of changes in potential around any closed loop involving resistors and cells is zero.

Wheatstone Bridge

An arrangement of four resistors used to determine an unknown resistance; the balance condition for zero galvanometer current is $\frac{R_2}{R_1} = \frac{R_4}{R_3}$.

Ohmic Loss

The power dissipated as heat in a conductor of resistance $R$ carrying current $I$, given by $P = I^2 R = \frac{V^2}{R}$.